Tray loading is the application where the usual gripper arithmetic stops being useful. The products are light, often only grams each, so holding force is almost never the constraint. What constrains the cell is how many items you can pick per cycle, how precisely their spacing matches the tray, and whether every cup in the array seals at the same instant.
That shifts the design problem. Instead of asking how much force the tool needs, you end up asking how many picks it has to make at once and what pitch they arrive at. Here is how those two questions shape a multi-pick tool.
What Is Tray Loading?
Tray loading is the automated placement of multiple products into a tray, carton or cavity pack, usually many units per cycle and usually at a fixed spacing set by the tray. It appears across food, medical device, cosmetics and consumer goods packaging, wherever product arrives in a stream and has to leave in a grid.
The defining characteristic is count rather than mass. A tool that places two dozen items per cycle is doing two dozen separate gripping operations simultaneously, and every one of them has to succeed. A single failed seal in an array of 24 is a failed cycle, which is why reliability per cup matters far more here than raw capacity.
Cup Count Is Not the Same as Holding Force
Adding cups to an array does not proportionally add holding force, and on light products it usually adds none that you needed. Holding force comes from effective sealing area multiplied by the pressure difference across it, so the force a cup contributes depends on how much area it genuinely seals, not on how many cups are bolted to the plate.
The pressure side of that is bounded by atmosphere. One standard atmosphere is 101.325 kPa, as NIST defines it, and a real circuit only ever achieves part of that, so there is a hard ceiling on force per unit of sealed area no matter what you do to the vacuum source. Force is bought with area and with seal quality, and nothing else.
| Factor | What it changes | Why |
|---|---|---|
| Adds holding force | Larger effective sealing area per cup, and a deeper vacuum level | A cup only contributes the area it actually seals, so a bigger cup on a flat surface beats two small ones on a curved one |
| Does not add holding force | More cups on a product too small or too light to need them | Extra cups on the same item add sealing area you were never short of |
| Consumes the gain | Poor seal, porous or textured surface, product flex under load | A cup that leaks contributes flow, not force |
| Sets the real limit on light products | Evacuation time and seal quality, not force | You reach the cycle ceiling long before you reach the force ceiling |
The conclusion for tray loading is worth stating plainly, because it inverts the usual sizing logic: on a high count, low weight array you add cups to cover more items, not to hold each item harder. The cup count is set by the pick pattern. The cup size and type are set by the product surface. Those are two separate decisions, and conflating them is how tools end up heavier and slower than they needed to be. Our vacuum gripper guide covers the force side in more general terms.
Pitch Matching: The Constraint That Shapes the Tool
Pitch is the centre to centre spacing between picks, and on a tray loading cell there are usually two of them that do not agree. Product arrives on a conveyor or from an infeed at one spacing, and the tray needs it at another. Reconciling those two numbers is the single biggest driver of tool architecture.
If both pitches are fixed and identical, the tool is simple: a rigid array at that spacing, picked and placed as one unit. That is the cheapest and fastest option and it is worth designing the upstream equipment to allow it wherever you can.
When the two pitches differ, something has to change spacing mid-cycle. A variable pitch or spreader tool expands and contracts the array between pick and place, which is how one tool serves an infeed spacing and a tray spacing at once. Our spreader end-of-arm tool write-up covers that mechanism in detail. The alternative is indexing, picking a partial row and placing it in several moves, which costs cycle time and is usually the fallback rather than the plan.
One detail that catches people: tray cavity spacing is not always as consistent as the drawing suggests. Thermoformed trays vary with the forming process and with temperature, so an array sized to nominal pitch can fight the tray at the ends of a long row. Cup compliance absorbs some of that, and it is worth measuring real trays rather than trusting the print.
Designing the Multi-Pick Array
Three decisions define a tray loading array, and they interact.
Zoning. An array that is valved as one zone succeeds or fails as one unit. Splitting it into independently valved groups lets the tool place a partial row when the infeed is short, which on a line with variable upstream supply is the difference between running and stopping. The cost is more valves, more tube and more mass at the wrist.
Compliance. Every cup has to reach its product even though products vary in height and the tool is rigid. Sprung or bellows cups absorb that variation individually, which matters far more on a 24 cup array than on a 4 cup one, because the tallest and shortest item in the group set the range the tool has to swallow.
Mass. A large array at full reach is mostly plate, and plate is weight. Printing the array lets the vacuum route inside the structure rather than through external fittings and lets material sit only where load requires it, which is the same logic behind most of the end-of-arm tooling we build. On a high cycle tray loader, tool mass is directly a throughput number.
Product Contact, Marking and Release
Light products bring problems that heavy ones do not. A thin lidding film, a soft tub or a printed surface can be marked by a cup that would be entirely safe on a case of bottles, and marking is a quality reject rather than a handling failure, so it often goes unnoticed until a customer complains.
Cup choice is the main lever. A larger, softer cup spreads the same load over more area and marks less, which is the opposite of the instinct to fit the smallest cup that will fit the product. Where the surface will not tolerate a cup at all, the answer is usually to grip a different feature of the product rather than to reduce vacuum.
Release is the other half. A light product does not fall away when vacuum stops, because residual vacuum and static hold it against the cup long enough to land out of position. Positive blow off solves it, and on a high count array the blow off has to reach every cup at the same time or the pattern lands unevenly. Food contact applications add their own constraints, as in our food grade salad tub gripper case study.
How We Approach Tray Loading Tools
We are Anubis 3D Industrial Solutions. We design and manufacture end-of-arm tooling and produce it by selective laser sintering at our facility in Mississauga, Ontario, and tray loading arrays are one of the clearest cases for printing rather than fabricating a tool.
The reason is that a multi-pick array is mostly internal air routing. Printing it puts the vacuum manifold inside the plate, removes the external tube runs that would otherwise crowd a tight pitch, and keeps the whole assembly light enough for a fast cycle. Where the array needs to be reconfigured for a different tray, modular area surface gripper components cover part of that range without a new tool.
Tray Loading Questions
What is tray loading in packaging?
Tray loading is the automated placement of multiple products into a tray, carton or cavity pack, usually many units per cycle at a spacing fixed by the tray. It is common in food, medical device and consumer goods packaging.
Does adding more suction cups increase holding force?
Only if the extra cups add effective sealing area you actually needed. Holding force is sealing area multiplied by the pressure difference, so cups that do not seal well, or cups added to an already adequately held product, contribute nothing useful. On light tray loading products the cup count is set by how many items you pick, not by force.
How do you handle different pitches between infeed and tray?
Either design the upstream equipment so both spacings match, which gives the simplest and fastest tool, or use a variable pitch spreader tool that expands and contracts the array between pick and place. Indexing in several partial moves is the slower fallback.
Why do light products get marked during tray loading?
Usually because the cup is too small, concentrating the load over a small contact area on a thin or printed surface. A larger, softer cup spreads the same load and marks less. Residual vacuum at release can also drag a light product out of position, which positive blow off fixes.
Working Out a Tray Loading Array?
Send us the product, the infeed spacing, the tray layout and the cycle you need, and our team will work out the cup count, the pitch strategy and whether you need a spreader or a fixed array.
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